Liquids such as milk that must be periodically agitated are typically stored in tanks which include agitators or stirrer assemblies. Such tanks are also sometimes referred to as stirrer tanks. In addition to including agitator assemblies, such tanks usually must also be designed to facilitate internal cleaning for sanitary purposes. In the case of liquid food products, such as milk for example, both the interior of the tank and the agitator assembly must be cleaned periodically. Good sanitary tank design requires the product agitators to be as cleanable as the internal tank surface.
Devices have been available heretofore for cleaning such tanks. For example, U.S. Pat. No. 4,168,918 to DeJonge shows such a device wherein cleaning fluid is introduced through a hollow drive shaft with spray nozzles thereon which direct the fluid against opposite sides of the impeller and the inside of the seal in the tank wall surrounding the shaft. Two hollow coaxial shafts are utilized; one of which is outside the tank and coupled to the drive motor, and the other of which extends into the tank and connects the drive shaft to the impeller. The inside shaft is mounted so as to be easily removable from the drive shaft in order to clean the nozzles therein. At least some manual intervention in the form of disassembly, scrubbing or brushing, and reassembling part of the agitator, is necessary to effect thorough cleaning of the tank and the agitator assembly before reuse. This is time consuming and thus expensive.
Another approach has been to inject cleaning solution into the tank past a seal surrounding the tool shaft. For example, in the TEBEL OST-III, the tool shaft extends completely across the tank and is supported at one by the drive shaft and at the opposite end by a sliding bearing. The tool and drive shafts are keyed together for rotation in unison. The sanitary seal assembly consists of a pair of circumferential lip seals with a drained space or chamber between the seals. During cleaning, the seal assembly is flushed from the inside by forcing cleaning solution into the chamber and past the inner seal into the tank. Thus, whereas in the system shown in the DeJonge patent cleaning solution is sprayed onto the inside of the inner seal, in the TEBEL system cleaning solution is forced past the inner seal from the outside to the inside of the tank. There is no provision, however, in the TEBEL system for directing cleaning solution onto or past the bearing at the opposite end of the shaft, which must be brushed or scrubbed by hand to effect thorough cleaning.
The prior art has thus been characterized by partial disassembly of the agitator assembly and/or manual scrubbing to effect thorough cleaning of the interior of a tank. A need has thus developed for an improved agitator assembly which is constructed so as to facilitate cleaning of the portion of the housing surrounding the tool shaft internal to the tank, the base of the impeller or agitator mounted on the end of the tool shaft, and the seal between the shaft and the internal housing, without manual intervention.